For example, Japanese Patent Publication (kokoku) No. H7-84850 discloses a known driving force controller for a vehicle, such as an automobile, in which a spark ignition engine is mounted, the driving force controller controlling driving force of the vehicle through control of throttle opening of the engine and control of ignition timing. When drive slippages of drive wheels increase, the driving force controller lowers the output of the engine through control of fully closing the throttle valve and control of delaying the ignition timing, to thereby reduce the driving force of the vehicle. When the drive slippages of drive wheels decrease, the driving force controller first stops the control of delaying the ignition timing, and then stops the control of fully closing the throttle valve.
When the ignition timing is delayed in control of the spark ignition engine, the output of the engine can be reduced with good responsiveness, whereby the driving force of the vehicle can be reduced with good responsiveness. However, when the ignition timing is delayed, the temperature of exhaust gas of the engine increases, which causes deterioration of an exhaust gas purification catalyst. Therefore, the ignition timing cannot be delayed continuously, and a period over which the control for delaying the ignition timing is performed is restricted to a short period of time.
In contrast, when the output of the engine is reduced through the control of completely closing the throttle valve, the temperature of exhaust gas of the engine does not increase, and, thus, deterioration of the exhaust gas purification catalyst does not occur. Therefore, the control of completely closing the throttle valve can be performed continuously. However, the control of completely closing the throttle valve cannot reduce the output of the engine with good responsiveness, and, thus, cannot reduce the driving force of the vehicle with good responsiveness.
However, the driving force controller disclosed in the above-described Japanese Patent Publication No. H7-84850 does not take into consideration the execution time of the ignition-timing delay control, and may cause an increase in the temperature of exhaust gas of the engine and resultant deterioration of the exhaust gas purification catalyst. Therefore, the driving force controller disclosed in Japanese Patent Publication No. H7-84850 has a problem of being unable to clear strict emission control standards enacted in recent years.
Japanese Patent Application Laid-Open (kokai) No. H10-264801 discloses a driving force controller in which the execution time of the ignition-timing delay control is restricted. However, since execution of the ignition-timing delay control is restricted to a predetermined period of time which starts from a point in time when reduction of the engine output through control of reducing the throttle opening is started, the execution time of the ignition-timing delay control must be restricted to a very short time in order to prevent an increase in the temperature of exhaust gas of the engine in all travel conditions of the vehicle. Accordingly, the driving force controller has a problem that the effect of reducing the vehicle driving force through the ignition-timing delay control is limited. Such a problem arises, for example, in the case where drive slippages of the drive wheels occur immediately after the vehicle has started to move, the throttle-opening reduction control and the ignition-timing delay control are started in order to cope with the drive slippages, and the ignition-timing delay control is ended after elapse of a predetermined time. In such a case, even when drive slippages of the drive wheels continuously occur after that point in time, the ignition-timing delay control cannot be executed, and the drive slippages cannot be effectively reduced by means of reducing the engine output through the ignition-timing delay control.
Further, as in the case of the ignition-timing delay control, through reduction of the amount of fuel supplied to the engine, the output of the engine can be reduced with higher responsiveness as compared with the case of the throttle-opening reduction control. However, when the amount of fuel supplied to the engine is reduced, as in the case of the ignition-timing delay control, the temperature of exhaust gas of the engine increases, which causes deterioration of the exhaust gas purification catalyst. Accordingly, the execution time of the control of reducing of the fuel supply amount must be restricted to a very short time.